Oct. 31 marked the 30th anniversary of the Pregnancy Discrimination Act (PDA), which outlaws job discrimination against moms-to-be. But the news that pregnant women need to be treated as any other worker with a temporary disability—you know, not get fired or demoted—hasn't fully registered with some employers, Time magazine reports.

Working U.S. women are filing more pregnancy-bias complaints, according to a new study from the National Partnership for Women & Families. The study found that women in 2007 filed 65 percent more grievances (5,587) with the U.S. Equal Employment Opportunity Commission compared to 3,385 cases in 1992.

Filings from women of color and employees in female-dominated fields fueled the increase—75 percent of the 50,277 total complaints between 1997 and 2007. The National Partnership for Women & Families notes discrimination grievances have risen at a faster rate than the influx of women into the workplace.

Time magazine quotes one legal expert about the misconceptions and possible reasons behind the rising bias cases: There's the underlying assumption that a woman won't be as interested or committed to her work when she becomes a mom; there's an urge to "do the right thing" and lessen a mom-to-be's duties; and financially, her insurance will be more expensive and she'll have to take some leave. The National Partnership for Women & Families said people may feel like they're doing the right thing, but they're not in the long run.

The report urges targeting select industries and increasing outreach to employers and workers to educate them on the law and anti-discrimination policies.